A new type of artificial lung is under development and evaluation. This extracorporeal device is based on principles of hemodialysis. Oxygenation is achieved by transmembrane catalysis of H2O2. Carbon dioxide excretion is obtained by dialyzing out bicarbonate ion. The associated production of buffered hydrogen ion is neutralized by placing sufficient hydroxyl ion in the dialysis bath to counter diffuse into the blood compartment to maintain normal pH. Transmembrane catalysis of H2O2 is achieved by deposition of ruthenium oxide or ruthenium sulfide in a regenerated celluosic hemodialysis membrane. Sufficient catalyst is deposited so as to completely prevent H2O2 from contacting blood. Using these catalyst impregnated membranes a high efficiency membrane oxygenator has been designed and tested. Blood moves between a layer of membranes formed into rills perpendicular to blood flow ("Oxford" oxygenator). This geometry results in secondary flows which improve O2 transport in the blood. This effect is further enhanced by intermittent partial reverse blood flow. The in vitro and animal experiments indicate that the design flow of 2-3 L/min/M2 for both O2 and CO2 is obtainable.